The present invention relates to fluid transfer devices, and more particularly to a base component for a hydraulic hand pump and the method of making such a component.
Various types of fluid transfer devices are known. Examples of such devices include hydraulic hand pumps, cylinders and directional control valves all of which are useful in a wide variety of industries such as the construction and mining industries. The base components for such pumps, cylinders and valves are typically constructed of cast iron with the appropriate internal circuitry machined therein. However, cast iron is relatively heavy and this weight is undesirable for hand pumps which are designed to be portable. Additionally, cast iron readily conducts electricity and this characteristic is undesirable in some environments for safety reasons. Further, cast iron subjects machining tools to relatively high abrasive wear and is thus more expensive to machine than other metals such as aluminum. Also, molds for iron castings have a life expectancy which is significantly less than molds used with other types of materials such as plastic. This increases the relative cost of manufacturing when employing cast iron. It is therefore desirable to reduce the weight of such fluid transfer devices by employing lighter weight materials such as aluminum and moldable plastic and also take advantage of the reduced manufacturing costs accompanying the use of such materials.
One of the basic design criteria for a fluid transfer device is to employ a material of construction for the base or core components that will withstand the relatively high internal pressure developed during operation. Additionally, the material of construction must be able to withstand external structural loads applied against members projecting integrally from the base or core, as for example, the load applied against the integral yoke of a hand pump during the reciprocal movement of a piston and handle assembly, and be moldable or castable into various shapes. In the past these criteria necessitated the use of cast iron instead of cast aluminum or molded plastic since constructing a solid base or core component from these latter two materials resulted in relatively large voids which in turn diminished the structural integrity of the device. The use of projecting integral members also prevented the use of less expensive extrusion processes. It is therefore desirable to develop a fluid transfer device that would employ a base or core component made of extruded aluminum to withstand internal pressure, and projecting integral members of moldable plastic to take the external structural loads on the device.
Insert molding is well-known in the art. One type of insert molding employs a molding process wherein a cylindrical metal bushing is molded directly into a plastic component during the molding operation. The bushing is typically used with a fastener to prevent failure or fatigue cracking of the plastic material which would otherwise take the load when the component is fastened to another structure.
Encapsulation processes employing a moldable plastic material are also well-known in the art as shown by U.S. Pat. No. 2,618,689, as is the molding of plastic components in a mold utilizing a preform as the core of the mold as shown in U.S. Pat. No. 3,355,772.